1. Field of the Invention
The present invention relates to a recording thin film magnetic head used for, for example, a floating magnetic head and the like. Particularly, the present invention relates to a thin film magnetic head which is adaptable to a narrower track, and in which a track width can be precisely formed to a predetermined dimension, a magnetic path can be shortened, and a leakage of a magnetic flux can be suppressed to improve recording characteristics, and a method of manufacturing the thin film magnetic head.
2. Description of the Related Art
FIG. 25 is a longitudinal sectional view showing an example of conventional thin film magnetic heads, in which the leftmost surface shown in parallel to a X-Z surface on the left side of the drawing is a “surface facing a recording medium”. In FIG. 25, the X direction coincides with the track width direction, the Y direction coincides with the height direction, and the Z direction coincides with the movement direction of a magnetic recording medium such as a hard disk or the like.
In FIG. 25, reference numeral 1 denotes a lower core layer made of a NiFe alloy, and reference numeral 2 denotes a gap layer made of Al2O3 or the like and formed on the lower core layer 1. As shown in FIG. 25, a coil layer 3 made of Cu is formed on the gap layer 2 and coated with an organic insulating layer 4 made of resist or the like. Also, an upper core layer 5 made of a NiFe alloy or the like is formed on the organic insulating layer 4, the front end 5a of the upper core layer 5 facing the lower core layer 1 with the gap layer 2 provided therebetween near the surface facing the recording medium, and the base end 5b being formed in direct contact with a rear portion of the lower core layer 1 in the height direction.
FIG. 26 is a longitudinal sectional view of another example of conventional thin film magnetic heads, and FIG. 27 is a front view of the thin film magnetic head shown in FIG. 26. In FIG. 26, the surface shown on the left side of the drawing is a “surface facing a recording medium”.
In FIG. 26, reference numeral 6 denotes a lower core layer which contains a protrusion 6a protruding toward an upper core layer (the Z direction shown in the drawing) near the side facing the recording medium. As shown in FIG. 26, a back gap layer 7 made of a magnetic material is formed on a rear portion of the lower core layer 6 in the height direction (the Y direction), and a coil layer 8 is partially disposed between the protrusion 6a and the back gap layer 7. The coil layer 8 is covered with an insulating layer 9, and the top 6b of the protrusion 6a, the top 9a of the insulating layer 9 and the top 7a of the back gap layer 7 are planarized.
As shown in FIG. 26, a gap layer 10 made of Al2O3 or the like is formed to extend from the top 6b of the protrusion 6a to the top 9a of the insulating layer 9, and a nonmagnetic layer 12 is formed on the gap layer 10 to extend from a position at a predetermined distance from the surface facing the recording medium in the height direction. Furthermore, an upper core layer 11 is formed over the gap layer 10, the nonmagnetic layer 12 and the back gap layer 7.
FIG. 28 is a longitudinal sectional view showing a further example of conventional thin film magnetic heads. In FIG. 28, the surface shown on the left side of the drawing is a “surface facing a recording medium”.
In FIG. 28, reference numeral 13 denotes a lower core layer which contains a protrusion 13a protruding toward an upper core layer (the Z direction shown in the drawing) near the surface facing the recording medium. As shown in FIG. 28, a back gap layer 14 made of a magnetic material is formed on a rear portion of the lower core layer 13 in the height direction (the Y direction), and a coil layer 15 is partially disposed between the protrusion 13a and the back gap layer 14. The coil layer 15 is covered with an insulating layer 16, and the top 13b of the protrusion 13a and the top 16a of the insulating layer 16 are planarized. As shown in FIG. 28, a gap layer 18 made of, for example, Al2O3 is formed on the top 13b of the protrusion 13a and the top 16a of the insulating layer 16 to extend from the surface facing the recording medium to the front end 14a of the back gap layer 14, and the top 18a of the gap layer 18 and the top 14b of the back gap layer 14 are planarized.
Furthermore, an upper core layer 19 is formed over the top 18a of the gap layer 18 and the top 14b of the back gap layer 14.
These thin film magnetic heads are disclosed the following patent documents.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 2001-319311
[Patent Document 2]
Japanese Unexamined Patent Application Publication No. 2001-250203
In recent years, decreases in size requirements have resulted in some amount of miniaturization of the thin film magnetic heads. In addition to miniaturization requirements, increases in operating speed requirements coupled with increases in the recording density and frequency (as well as reductions in size) have resulted in more stringent requirements for design structures, material properties, and other characteristics of the thin film magnetic heads.
In the thin film magnetic head, the width dimension and, more specifically, the track width, decreases as the recording density increases. The track width Tw is the width of the front end 5a of the upper core layer 5 at the surface facing the recording medium.
However, when the organic insulating layer 4 formed to cover the coil layer 3 extends from the gap layer 2, as shown in FIG. 25, the resist used for patterning the upper core layer 5 is influenced by irregularities introduced during processing, e.g. irregular reflection during development. Such irregularities appear in conventional thin film magnetic heads. The upper core layer 5 of conventional thin film magnetic heads thus cannot be formed in a predetermined shape, which consequently increases the track width Tw.
In addition, conventional thin film magnetic heads, like that shown in FIG. 25, must have a low thermal expansion coefficient. If a thin film magnetic head has a high thermal expansion coefficient, thermal deformation occurs during driving. In particular, the gap layer 2 or the like projects from the surface facing the recording medium when such thermal deformation occurs. This causes the spacing, i.e. the distance from the surface facing the recording medium (not shown) to the surface of the recording medium, to decrease. While a decrease in spacing in general permits a higher recording density to be realized, it is undesirable in this case as the projection of the gap layer 2 or the like causes collision between the thin film magnetic head and the recording medium during driving.
In addition, the same results can occur if enough of a mismatch exists between the thermal expansion coefficients of the different layers. For example, the thin film magnetic head shown in FIG. 25 contains the organic insulating layer 4 made of resist, for covering the coil layer 3. Since the organic insulating layer 4 has a significantly higher thermal expansion coefficient than the thermal expansion coefficients of the other layers, the organic insulating layer 4 thermally expands during driving of the thin film magnetic head, and thus the gap layer 2 projects toward the recording medium due to the expansion.
In the thin film magnetic head shown in FIG. 25, the magnetic path extending from the upper core layer 5 to the lower core layer 1 is long because the organic insulating layer 4 covers and extends a significant distance from the gap layer 2. Due to the length of the magnetic path, the coil layer 3 must have a certain turn number in order to obtain the necessary flux efficiency. A reduced number of turns decreases the heat generated by a comparable amount and thus expansion of the organic insulating layer 4. However, because the coil resistance in this conventional structure cannot be decreased, the projection remains problematic in such a structure.
In the thin film magnetic head shown in FIG. 26, the coil layer 8 is buried in the space formed by the lower core layer 6, the protrusion 6a and the back gap layer 7, and thus the thickness of a layer (the nonmagnetic layer 12) disposed on the gap layer 10 is smaller than that in the thin film magnetic head shown in FIG. 25, thereby facilitating precise formation of the upper core layer 11 in comparison to the thin film magnetic head shown in FIG. 25. However, the upper core layer 11 is not formed on a completely planarized surface, and thus the upper core layer cannot be precisely formed in a predetermined shape, as above consequently increasing the track width Tw.
The thin film magnetic head shown in FIG. 26 also has the following problem: in order to suppress side fringing, the front side of the thin film magnetic head must be trimmed to the shape shown in FIG. 27. The side fringing is a phenomenon in which the track width is substantially increased by leakage of a magnetic field from both sides. Because of the increase in recording density, side fringing must be prevented as much as possible.
Therefore, as shown in FIG. 27, both side ends 11a of the upper core layer 11, both side ends 10a of the gap layer 10 and both side ends 6c of the protrusion 6a of the lower core layer 6 are trimmed to set the track width Tw to the greatest extent possible.
However, the required track width Tw is as small as about 0.3 μm or less. This width is, at the least, difficult to reach by trimming. Also, readhesion after trimming decreases precision of the track width Tw, which increases in importance as the track width Tw decreases.
Unlike the thin film magnetic head shown in FIG. 26, in the thin film magnetic head shown in FIG. 28, a nonmagnetic layer is not formed on the gap layer 18. Therefore, the top 18a of the gap layer 18 and the top 14b of the back gap layer 14 can be planarized, and thus the upper core layer 19 can be formed on the planarized surface, thereby facilitating the precise formation of the upper core layer 19 in comparison to the thin film magnetic head shown in FIG. 26.
However, like in the thin film magnetic head shown in FIG. 26, in the thin film magnetic head shown in FIG. 28, both side ends of the upper core layer 19, both side ends of the gap layer 18 and both side ends of the protrusion 13a in the track width direction are trimmed to set the track width Tw. Therefore, as described above with reference to FIG. 27, the track width Tw cannot be easily precisely defined due to readhesion during trimming.
In addition, in the thin film magnetic head shown in FIG. 28, the gap layer 18 is formed from an inorganic insulating material such as Al2O3. The gap layer 18 must not be formed at a connection between the back gap layer 14 and the upper core layer 19. Therefore, as shown in FIG. 28, the gap layer 18 is absent from the connection between the back gap layer 14 and the upper core layer 19. In manufacturing the structure shown in FIG. 28, a through hole for forming the back gap layer 14 must be formed in the gap layer 18 and the coil insulating layer 16 after the gap layer 18 is formed, and then the back gap layer 14 must be formed in the through hole by plating, complicating the manufacturing process. Particularly, if the through hole does not completely extend from the top 18a of the gap layer 18 to the surface of the lower core layer 13, magnetic connection between the lower core layer 13 and the back gap layer 14 deteriorates, thereby deteriorating the recording properties. However, as the coil insulating layer 16 is relatively thick, it is difficult to form a through hole that completely passes through the coil insulating layer 16.
As described above, the thin film magnetic heads shown in FIGS. 25, 26 and 28 are limited in both recording density and frequency. Thus, thin film magnetic heads having a higher recording density and higher frequency cannot be provided in the future, and the recording properties of the thin film magnetic heads cannot be improved.